1. Field of the Invention
The present invention generally relates to color cathode ray tubes and, more particularly, to a color cathode ray tube utilizing a flat tension shadow mask.
2. Description of the Prior Art
FIGS. 8 and 9 of the accompanying drawings are schematic reproductions of a prior art color cathode ray tube of a type disclosed in, for example, the Japanese Laid-open Patent Publication No. 61-80735, being laid open to public inspection on Apr. 24, 1986; U.S. Pat. No. 4,547,696, patented Oct. 15, 1985; SID 86 DIGEST, PAGES 322-326; and Information Display, October 1986, pages 43-44, wherein FIG. 8 is a schematic top plan view, with a portion cut away, of the prior art color cathode ray tube and FIG. 9 is a fragmentary sectional view, on an enlarged scale, of the prior art cathode ray tube shown in FIG. 8.
As shown therein, the color cathode ray tube comprises a highly evacuated glass envelope having a generally rectangular faceplate 11 and a generally rectangular frame-shaped skirt 12 bonded at 3 to the faceplate 11 by means of beads of glass frit so as to protrude from a peripheral portion of the faceplate 11, said faceplate 11 having formed on an inner surface a phosphor screen 11A which is made up of luminescent phosphor deposits which may be arranged in triads of red, green and blue phosphor dots. The envelope also has a funnel 4 having one end bonded at 14 to the skirt 12 by means of beads of glass frit and a neck 5 protruding from the opposite, tapered end of the funnel 4, the free end of said neck 5 being closed by an electrode carrier stem while a well known electron gun assembly has been installed inside the neck 5.
A color selecting shadow mask 2 having a predetermined pattern of apertures 2a formed by the use of an etching technique, which apertures 2a can be triads of minute holes is supported with its peripheral portion secured to the skirt 12 and is, while tensed uniformly over the entire surface area thereof, positioned so as to confront the phosphor screen 11A. With the shadow mask 2 so positioned, the apertures of the shadow mask 2 are registered with, and patterned relative to, the phosphor dots on the phosphor screen 11A so that each triad of red, green and blue electron beams emitted from an electron gun assembly and passing through a particular aperture 2a can impinge upon the associated triad of red, green and blue phosphor dots.
When in use, the red, green and blue electron beams emitted from the electron gun assembly pass through the apertures 2a in the shadow mask 2 and then impinge upon the phosphor screen 11A, formed on the inner surface of the faceplate 11, to cause the associated triads of phosphor deposits or dots to emit light. Considering the role of the shadow mask to shadow, i.e., mask, the phosphor screen from being scanned by the electron beams to achieve a color selection, a portion of the electron beams impinges upon a non-apertured area of the shadow mask 2 at the time the electron beams pass through the associated apertures in the shadow mask, causing the localized heating of the shadow mask 2. Consequent upon the heating of the shadow mask 2, the latter undergoes a thermal expansion with the shadow mask 2 tending to deform.
However, since the shadow mask 2 is held under tension to maintain flatness sufficient to compensate for the amount of thermal deformation thereof, the possible thermal deformation of the shadow mask can be counteracted by the tension imparted on the shadow mask, thereby to minimize any change in pitch between each neighboring apertures in the shadow mask so that any possible mislanding, i.e., incorrect landing, of the electron beams on the phosphor screen 11A can be minimized. The minimization of the mislanding of the electron beams on the phosphor screen is essential to ensure a high quality reproduction of the televised pictured on the screen.
Since the prior art color cathode ray tube referred to above is of three-piece construction wherein the faceplate 11, the skirt 12 carrying the shadow mask 2 and the funnel 4 including the neck 5 are separate from each other and bonded together to complete the envelope, the manufacture of the envelope requires separate processing steps for the molding of the faceplate 11, the skirt 12 and the funnel 4. In other words, the manufacture of the envelope for the prior art color cathode ray tube requires an increased number of processing steps not only for the glass molding, but also for the bonding of the components together, with the consequence that the productivity tends to be lowered.
As hereinabove discussed, the prior art color cathode ray tube of the construction described above brings about problems of lowering the production yield, that of the preciseness of fabrication and, hence, the reliability, and increase of the manufacturing cost.
Apart from the above discussed prior art color cathode ray tube, the cathode ray tube utilizing the flat faceplate integrally formed with the skirt by the use of a press-molding technique is also well known in the art. The use of the press-molding tends to result in the occurrence of a "suction" phenomenon, a localized buckling of the faceplate resulting from the vacuum suction which occurs when the faceplate as molded is separated from a mold assembly. As a result, the faceplate cannot be formed precisely flat.